This invention relates generally to a magnetic recording and reproducing system, and more particularly to a magnetic recording and reproducing system with a composite magnetic head comprising a combination of a ferromagnetic metal and a high permeability ferrite single crystal.
There is an extremely strong demand nowadays for an improved magnetic recording technique, particularly for magnetic recording of higher density.
It is well known in the art that to satisfy this demand, it is advantageous to increase the coercive force Hc of a magnetic recording medium. However, a magnetic field having a greater field intensity and a sharp distribution is necessary to record signals on a magnetic recording medium having high coercive force.
When ferrite material having a high permeability, which has been widely used in the past, is used for a magnetic head, its saturation flux density Bs is below 5,500 gauss so that there is an inevitable limitation to the intensity of the resulting recording magnetic field. Moreover recording is inadequate, particularly when a high coercive force magnetic tape, which has been recently developed, is used as the recording tape.
Materials having a great saturation flux density include heretofore known ferromagnetic metals such as Fe-Al-Si system alloys, Fe-Ni system alloys, Fe-Si system alloys, ferromagnetic amorphous alloys, and the like, but when these ferromagnetic metals are used alone for the magnetic head, the service life of the head is short because the surface facing the magnetic recording medium (hereinafter, sometimes, abbreviated as sliding surface) exhibits a high wear rate, and production of the head is difficult.
To eliminate the problems described above, a composite magnetic head has been proposed (e.g., Japanese Patent Laid-Open Nos. 159818/1981 and 155513/1983). This composite magnetic head has a construction in which the surface facing the magnetic recording medium is composed at least of a ferromagnetic metal and a high permeability ferrite, and the region near the gap is composed of a ferromagnetic metal having a high saturation flux density.
Since the region of the composite magnetic head near the gap is composed of a ferromagnetic metal having a high saturation flux density, the head exhibits excellent recording characteristics, and since at least a part of other regions of the surface facing the recording medium is composed of a high permeability ferrite having high wear resistance and high permeability at a high frequency, the head has high reproducing efficiency and high wear resistance.
However, if the surface facing the magnetic recording medium is composed of a high permeability ferrite having high wear resistance and a ferromagnetic metal having lower wear resistance than the former, the surface of the ferromagnetic metal is recessed more deeply than the surface of the high permeability ferrite due to wear caused by the travel of the magnetic recording medium in contact with said surfaces for an extended period of time; hence a step is formed between the two materials.
Because this step forms a small spacing between the magnetic recording medium and the ferromagnetic metal close to the gap, the output will deteriorate.
A recording wavelength tends to become shorter and the speed relative to the magnetic recording medium also tends to decrease due to the recent progress of high density magnetic recording. Therefore, the problem of the deterioration of the output due to the small spacing between, the head and the magnetic recording medium has become graver than the general wear of the head surface facing the magnetic recording medium.
When a composite magnetic head is employed, too, the problem of the small spacing resulting from the step described above is grave.
The following references are cited to show the state of art:
(1) Japanese Patent Laid-Open No. 159818/1981 PA1 (2) Japanese Patent Laid-Open No. 91517/1983 PA1 (3) Japanese Patent Laid-Open No. 155513/1983.